As it is generally known, labelling machines are used to apply labels to containers or articles of all sort. Typically used with beverage bottles or vessels are tubular labels (commonly called “sleeve labels”), which are obtained by:                cutting the web unwound from a supply roll into a plurality of rectangular or square labels;        bending each label in a cylindrical configuration such that the opposite vertical edges overlap one another; and        welding the overlapped edges of each cylindrical label.        
A particular type of labelling machine is known which serves to bend and weld labels in a tubular configuration and to produce insertion of containers into the so formed tubular labels. This kind of machine basically comprises a carousel rotating about a vertical axis to define a circular path, along which it receives a succession of unlabelled containers and, then, a succession of rectangular or square labels from respective input wheels, produces application of the labels in a tubular configuration onto the respective containers and releases the labelled containers to an output wheel.
More specifically, the carousel comprises a number of labelling units which are equally spaced about the rotation axis, are mounted along a peripheral edge of the carousel and are moved by the latter along the above-mentioned circular path.
Each labelling unit comprises a bottom supporting assembly adapted to support the bottom wall of a relative container and an upper retainer adapted to cooperate with the top portion of such container to hold it in a vertical position during the rotation of the carousel about the vertical axis.
Each supporting assembly comprises a vertical hollow supporting mount, secured to a horizontal plane of a rotary frame of the carousel, and a cylindrical receiving member, engaging the supporting mount in sliding and rotating manner with respect to its axis, and adapted to carry a relative container on its top surface and a relative label on its lateral surface.
Each receiving member can be displaced between a raised position and a fully retracted position within the relative supporting mount.
In the raised position, each receiving member protrudes from a top surface of the relative supporting mount and is adapted to receive a relative label on its lateral surface from the label input wheel; in particular the label is wrapped around the receiving member such that the opposite vertical edges of the label overlap one another.
In order to produce this complete wrapping, the receiving member is rotated about its axis during the transfer of the label from the label input wheel.
In the fully retracted position, which is reached at the container input and output wheels, the top surface of each receiving member is flush with the top surface of the supporting mount so that containers are transferred onto and from the carousel along the same transfer plane.
After the welding of the overlapped edges of a tubular label, the displacement of the relative receiving member from the raised position to the fully retracted position produces the insertion of the relative container inside the label, making the so obtained container ready to be transferred to the output wheel.
Each label is retained on the lateral surface of the relative receiving member by suction; in particular, at least a region of the lateral surface of each receiving member is provided with a plurality of holes in turn connected to a pneumatic suction device.
Such region normally has, in a direction parallel to the above-mentioned axis, an extension which is correlated to the height of the label to be processed.
This means that any change of the label format entails a replacement of all the receiving members of the labelling machine, with consequent high costs and long dismantlement and reassemble times.